The present invention relates to semiconductor fabrication and, more particularly, to a method for forming a contact hole by self aligned contact etching and a method for forming a plug inside the contact hole.
A recess channel gate improves a refresh property of a semiconductor device. The recess channel gate is formed as follows: forming a recess pattern on a substrate; forming a gate dielectric layer, a gate conductive layer and a second gate conductive layer over the recess pattern and the substrate; and then patterning the resulting structure using a gate patterning mask.
FIG. 1 illustrates micrographic views of an inner wall surface of a recess pattern that is exposed during the formation of a recess channel gate.
Referring to FIG. 1, during the patterning, misalignment between a mask for forming the recess pattern and the gate patterning mask often causes an inner wall surface 11 of the recess pattern to be exposed. This may cause cell threshold voltage mismatch of the recess channel gate and generate etch residue, thereby producing defects. In addition, the exposure of the inner wall surface of the recess pattern may cause a bridge phenomenon between the recess channel gate and a landing plug after subsequent processes.
To overcome these limitations, a method has been proposed for reducing a line width of the recess pattern and increasing the line width of the recess channel gate to increase an overlay margin.
However, if the line width of the recess channel gate is increased to increase the overlay margin, the aspect ratio of the recess channel gate is also increased. Thus, the open margin of the landing plug contact hole is decreased.
FIG. 2 illustrates micrographic views of a landing plug contact hole subject to a not-open phenomenon that is generated during a self aligned contact etching.
Referring to FIG. 2, the landing plug contact hole may not open as shown by reference numeral 12.
In addition, if an over etch is performed or the thickness of a barrier layer protecting the recess channel gate is decreased to increase the open margin of the landing plug contact hole, a bridge phenomenon may occur between the recess channel gate and the landing plug. Hereinafter, the phenomenon that causes the landing plug contact hole to not open is referred to as a ‘not-open defect’, and the bridge phenomenon that occurs between the recess channel gate and the landing plug is referred to as a ‘self aligned contact (SAC) failure.’
If the thickness of the barrier layer protecting the recess channel gate is increased to overcome the SAC failure, the not-open defect may be generated.